The present disclosure generally relates to peptides having adjuvant properties, vaccines comprising the adjuvant peptides, and their use in prophylaxis or therapy for influenza. More particularly, the invention relates to adjuvant peptides that induce aggregation of influenza virus. The peptides can be included in influenza vaccines to increase the immune response to the vaccine.
Outbreaks of influenza A virus continue to cause widespread morbidity and mortality worldwide. In the United States alone, an estimated 5 to 20% of the population is infected by influenza A virus annually, causing approximately 200,000 hospitalizations and 36,000 deaths. The establishment of comprehensive vaccination policies has been an effective measure to limit influenza morbidity. However, the frequent genetic drifting of the virus requires yearly reformulation of the vaccine, potentially leading to a mismatch between the viral strain present in the vaccine and that circulating. Thus, antiviral therapies against influenza virus are important tools to limit both disease severity as well as transmission.
The influenza virus is an RNA enveloped virus with a particle size of about 125 nm in diameter. It consists basically of an internal nucleocapsid or core of ribonucleic acid (RNA) associated with nucleoprotein, surrounded by a viral envelope with a lipid bilayer structure and external glycoproteins. The inner layer of the viral envelope is composed predominantly of matrix proteins and the outer layer mostly of host-derived lipid material. The surface glycoproteins neuraminidase (NA) and hemagglutinin (HA) appear as spikes, 10 to 12 nm long, at the surface of the particles. It is these surface proteins, particularly the hemagglutinin, that determine the antigenic specificity of the influenza subtypes.
Currently available influenza vaccines are either inactivated or live attenuated influenza vaccine, Inactivated flu vaccines are composed of three possible forms of antigen preparation: inactivated whole virus, sub-virions where purified virus particles are disrupted with detergents or other reagents to solubilize the lipid envelope (so-called “split” vaccine) or purified HA and NA (subunit vaccine). These inactivated or live attenuated vaccines are typically given intramuscularly (i.m.) or intranasally (i.n.).
Split or subunit injectable vaccines are prepared by disrupting the virus particle, generally with an organic solvent or a detergent, and separating or purifying the viral proteins to varying extents. Split vaccines are prepared by fragmentation of whole influenza virus, either infectious or inactivated, with solubilizing concentrations of organic solvents or detergents and subsequent removal of the solubilizing agent and some or most of the viral lipid material. Split vaccines generally contain contaminating matrix protein and nucleoprotein and sometimes lipid, as well as the membrane envelope proteins. Split vaccines will usually contain most or all of the virus structural proteins although not necessarily in the same proportions as they occur in the whole virus. Subunit vaccines on the other hand consist essentially of highly purified viral surface proteins, hemagglutinin and neuraminidase, which are the surface proteins responsible for eliciting the desired virus neutralizing antibodies upon vaccination.
Influenza vaccines, of all kinds, are usually trivalent vaccines. They generally contain antigens derived from two influenza A virus strains and one influenza B strain. A standard 0.5 ml injectable dose in most cases contains 15 μg of hemagglutinin antigen component from each strain, as measured by single radial immunodiffusion (SRD). The influenza virus strains to be incorporated into influenza vaccine each season are determined by the World Health Organization in collaboration with national health authorities and vaccine manufacturers.
One drawback to administration of influenza vaccines comprising inactivated virus is that such vaccines must typically be given in high concentrations in order to bring about a significant increase of antibodies. The administration of inactivated influenza virus or antigen in convenient commercial doses, free of side effects, does not always produce a satisfactory immune response, particularly when administered nasally or orally. As such, it is often necessary to include an adjuvant in the vaccine composition.
Recently, it has been shown that a 20-amino acid peptide derived from the fibroblast growth factor 4 (FGF-4) signal sequence and designated entry blocker (EB), displays significant broad-spectrum activity against influenza viruses in vitro and in vivo. The EB peptide has been described in Jones, et al., “Inhibition of Influenza Virus Infection by a Novel Antiviral Peptide That Targets Viral Attachment to Cells, Journal of Virology, (2006) Vol. 80(24), p. 11960-11967, and in U.S. Patent Application Publ. No. 2005/0130884 to Brandt, et al. and in U.S. Patent Application Publ. No. 2005/0203024 also to Brandt, et al. Specifically, it has been demonstrated that in vitro, EB inhibits virus replication at concentrations of 10 μM or greater. In BALB/c mice, EB prevented clinical signs of H5N1 influenza virus infection and increased survival when administered pre- or post-infection. It has also been established that EB inhibited influenza virus attachment to cells.
It has now been discovered that the EB peptide also acts as an effective influenza vaccine adjuvant by inducing viral aggregation, leading to increased viral uptake and processing by antigen presenting cells.